This proposal is for funds to purchase a Meridian ACAS 570 Interactive Laser Cytometer and accessories for NIH grant-funded basic research conducted in the Life Sciences Division (LSD) of SRI International (formerly Stanford Research Institute). The research goals require assessment of cellular characteristics such as cell-cell communication; intracellular calcium concentrations and distributions; antigen expression, distribution, transport and function; and resistance to therapeutic agents. ACAS 570 features vital to this research include capability to measure fluorescence recovery after photobleaching, adherent live cell sorting, laser cross-linking, quantitative fluorescence photometry, laser ablation of cells, and automated revisiting of cells of interest. The ACAS 570 will be integrated into an active research program investigating diverse aspects of basic cancer biology and experimental therapeutics, normal tissue biology, AIDS immunobiology, toxicology, and molecular neurobiology. This program requires studies of heterogeneous subpopulations of live cells to determine the importance of cell-cell and cell-microenvironmental interactions affecting responsiveness of cancer, normal or virus-infected cells to different therapeutics and factors affecting growth or differentiation. The major users of the ACAS 570 have extensive experience with related equipment (flow cytometry and centrifugal elutriation) or the ACAS 470. This equipment will be administered as a Shared Resource Facility of SRI, and the leaders of this program have played leading roles as Directors of successful Shared Resource Facilities. The projects proposed will draw on the many capabilities of the ACAS 570 to refine and extend this research in several new directions. This instrument will be used solely for basic research by (a) grant-funded senior scientists and other active collaborators of the LSD, of which Dr. Robert M. Sutherland (Principal Investigator) is the Director, who will collectively use approximately 80% of the instrument time, and b) other investigators of the LSD or other SRI Divisions (Bioengineering and Physical Sciences) who will utilize the remaining 20% time. The features of the ACAS 570 as related to the research needs of the major users and administrative organization and procedures to guarantee maximum utilization and scientific benefit from this equipment are described herein.